Fuel reforming apparatus

ABSTRACT

A fuel reforming apparatus includes a reaction tube for causing endothermic reaction for converting a fuel gas with hydrocarbon, steam, and the like mixed therein into a hydrogen-enriched gas using a catalyst, a combustor for generating a combustion gas for heating the reaction tube, a heat insulating layer for preventing the radiation of the combustion gas, and a combustion gas passage disposed around the reaction tube and allowing the combustion gas to flow therethrough, and a passage for air or fuel gas disposed around the fuel gas passage, a heat insulating layer being disposed around the outer peripheral surface of this passage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present relates to a fuel reforming apparatus, and, moreparticularly, to a fuel reforming apparatus suitable for use in afuel-cell power apparatus which is compact and of which rapidload-following characteristics are required.

2. Statement of the Related Art

A fuel reforming apparatus disclosed in U.S. Pat. No. 4,098,589, forinstance, is known as a fuel reforming apparatus for use in a fuel-cellpower apparatus which is compact and of which rapid load-followingcharacteristics are required, unlike fuel reforming apparatuses that areconventionally used in the chemical industry. In the fuel reformingapparatus of this patent, a reaction tube is made compact by improvingthe heat conductivity between the reaction tube on the one hand, and acombustion gas and a reforming gas on the other. Consequently, the fuelreforming apparatus is made compact and the load-followingcharacteristics are improved.

In the above-described prior art, a reaction tube is provided in acentral portion of a fuel reforming apparatus, and a combustion gas iscirculated through the reaction tube. These portions are surrounded by aheat insulating layer to prevent the radiation of heat. However, sincethe combustion gas and the heat insulating layer are disposed adjacentto each other, there has been a drawback in that the heat insulatinglayer tends to become thick, and the proportion of the heat insulatinglayer in the fuel reforming apparatus is large. In addition, thecombustion gas heats a wide area inside the heat insulating layer, andno consideration has hitherto been paid to the loss of the quantity ofheat of the combustion gas involved in the heating thereof.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a fuelreforming apparatus which is capable of making effective use of thequantity of heat of a combustion gas and which is compact.

In accordance with one aspect of the invention, there is provided a fuelreforming apparatus provided with an air passage which covers ahigh-temperature gas between a high-temperature combustion gas passageand the low-temperature open air.

In accordance with another aspect of the invention, there is provided afuel reforming apparatus provided with a supplying passage for fuel gasvia a heat-exchange wall between a heat insulating layer and acombustion gas passage so that the heat of the fuel gas issued from thecombustion gas passage to the outside of the reforming apparatus isimparted to the fuel gas passing through the supplying passage for fuelgas, whereby the heat from the combustion gas is utilized to promote thereforming reaction involving endothermic reaction.

According to still another aspect of the invention, there is provided afuel reforming apparatus having a reaction tube for causing endothermicreaction for converting a fuel gas with hydrocarbon, steam, and the likemixed therein into a hydrogen-enriched gas using a catalyst and a heatinsulating layer for preventing the radiation of the combustion gas, theapparatus comprising: a combustion gas passage disposed around thereaction tube and constituting a passage for the combustion gas; and asupplying passage for fuel gas disposed around the combustion gaspassage via a heat-exchange wall and constituting a passage for the fuelgas, the heat insulating layer being disposed around the outerperipheral surface of the supplying passage for fuel gas.

According to a further aspect of the invention, there is provided a fuelreforming apparatus having a reaction tube for causing endothermicreaction for converting a fuel gas with hydrocarbon, steam, and the likemixed therein into a hydrogen-enriched gas using a catalyst and a heatinsulating layer for preventing the radiation of the combustion gas, theapparatus comprising: a combustion gas passage disposed around thereaction tube and constituting a passage for the combustion gas; and asupplying passage for fuel gas which is disposed around the combustiongas passage via a heat-exchange wall and constitutes a passage for thefuel gas and in which the catalyst is filled, the heat insulating layerbeing disposed around the outer peripheral surface of the supplyingpassage for fuel gas.

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof the invention when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a fuel reforming apparatusin accordance with a first embodiment of the present invention;

FIG. 2 is a vertical cross-sectional view of a fuel reforming apparatusin accordance with a second embodiment of the present invention;

FIG. 3a is a vertical cross-sectional view of a fuel reforming apparatusin accordance with a third embodiment of the present invention;

FIG. 3b is a horizontal cross-sectional view taken along the lineIIIb--IIIb of FIG. 3a;

FIG. 4a is a vertical cross-sectional view of a fuel reforming apparatusin accordance with a fourth embodiment of the present invention;

FIG. 4b is a horizontal cross-sectional view taken along the lineIVa--IVa of FIG. 4a;

FIG. 5a is a vertical cross-sectional view of a fuel reforming apparatusin accordance with a fifth embodiment of the present invention;

FIG. 5b is a horizontal cross-sectional view taken along the line Vb--Vbof FIG. 5a;

FIG. 6a is a vertical cross-sectional view of a fuel reforming apparatusin accordance with a sixth embodiment of the present invention;

FIG. 6b is a horizontal cross-sectional view taken along the lineVIb--VIb of FIG. 6a;

FIG. 7a is a vertical cross-sectional view of a fuel reforming apparatusin accordance with a seventh embodiment of the present invention;

FIG. 7b is a horizontal cross-sectional view taken along the lineVIIb--VIIb of FIG. 7a; and

FIG. 8 is a vertical cross-sectional view of a fuel reforming apparatusin accordance with an eighth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a fuel reforming apparatus in accordance with a firstembodiment of the present invention. A reaction tube 4 of a double tubestructure which is constituted by an outer reaction tube 2 and an innerreaction tube 3 is provided in a central portion of this fuel reformingapparatus 1. One end of the outer reaction tube 2 is fluid-tightlyclosed. A catalyst supporting plate 5 is installed at an end of theinner reaction tube 3 which is located inside the outer reaction tube 2,and a reforming catalyst 6 is filled in a gap between the outer reactiontube 2 and the inner reaction tube 3. Incidentally, a hole 7 is providedin the catalyst supporting plate 5. An opening portion of the outerreaction tube 2 is jointed to a supporting plate 8, and a flow guide 9is secured to a bottom plate 11 at one end thereof. A guide wall 12 forcombustion gas is provided inwardly of the flow guide 9 with a spacetherebetween, and a flange provided at an upper end thereof is securedto the supporting plate 8. A combustion gas passage C is formed in aspace between the outer reaction tube 2 and the guide wall 12 forcombustion gas, and is connected to an exhaust tube 27. A heatinsulating member 14 is provided such as to be in contact with a lowerpart of an inner surface of the guide wall 12 for combustion gas. Acombustor 15 is disposed at a position surrounded by the heat insulatingmember 14. In the combustor 15, a number of nozzles 16 are disposed toface the bottom of the outer reaction tube 2. A supporting member 17,which also serves as a heat insulating member, is disposed at a lowerportion of the combustor 15 with a space between it and the bottom plate11. A fuel tube 19 for combustion is connected to the combustor 15 topenetrate the bottom plate 11 and the supporting member 17. An innerwall 20 of the reforming apparatus is provided at a position surroundingthe flow guide 9. The inner wall 20 of the reforming apparatus iscylindrical, and one end thereof is a flange 21, which is connected tothe bottom plate 11. Meanwhile, the other end of the inner wall 20 ofthe reforming apparatus is welded or bolted to an end plate 22 with thesupporting plate 8 placed therebetween. The end plate 22 is disposed ata position at which it covers the supporting plate 8 with a certain gapbetween it and the supporting plate 8. An air passage A is formed in thespace between the flow guide 9 and the inner wall 20 of the reformingapparatus. The inner reaction tube 3 penetrates a central portion of theend plate 22, and these members are welded and fixed together. One ofthe inner reaction tube 3 communicates with an exhaust tube 10 for rawfuel. An air supply tube 18 for introducing air into the air passage Ais provided in the bottom plate 11, while a raw fuel tube 25 forsupplying raw fuel is provided in the end plate 22.

Furthermore, a number of legs 28 for supporting the main body of thefuel reforming apparatus 1 are provided for the bottom plate 11. Thebottom plate 11, the inner wall 20 of the reforming apparatus, and theend plate 22 are covered with a heat insulating layer 29, and the fuelreforming apparatus 1 is thus arranged.

In this arrangement, although the inner reaction tube 3, the outerreaction tube 2, the guide wall 12 for combustion gas, the flow guide 9,and the inner wall 20 of the reforming apparatus are disposedconcentrically. However, a plurality of the reaction tubes of a doubletube structure may be provided.

In operation, combustion air is supplied from the air supply tube 18 tothe air passage A, while combustion fuel is supplied from the fuel tube19 to the combustor 15.

Flames are formed at the nozzles 16 and generate a high-temperaturecombustion gas. The combustion gas flows through the combustion gaspassage C between the guide wall 12 for combustion gas and the outerreaction tube 2 and is, while raising the temperature of the reactiontube 4 of a double tube structure and the reforming catalyst 6, led fromthe exhaust tube 27 to outside the fuel reforming apparatus 1.

Raw fuel to be reformed, such as methane, is mixed with steam, and isthen supplied through the raw fuel supply tube 25 and led into thereaction tube 4. The raw fuel is heated by the combustion gas, issubjected to the following endothermic reaction in a layer in which thereforming catalyst 6 is filled, and is thereby converted to ahydrogen-enriched gas:

    CH.sub.4 +H.sub.2 O→CO+3H.sub.2                     (1)

    CO+H.sub.2 O→CO.sub.2 +H.sub.2                      (2)

The hydrogen-enriched gas passes through the exhaust tube 10 for rawfuel and is exhausted to outside the fuel reforming apparatus 1.

The air flows through the air passage A and, at the same time, cools theflow guide 9, and the temperature of the air rises. The air which hascome out of the air passage A flows through a space formed by the flowguide 9 and the guide wall 12 for combustion gas and cools the guidewall 12 for combustion gas.

The provision of these air passages makes it possible to reduce thetemperature of the guide wall 12 for combustion gas, the flow guide 9,and the inner wall 20 of the reforming apparatus in that order and tomake the thickness of the heat insulating layer 29 thinner than in thecase where the air passages are not provided. In addition, since theguide wall 12 for combustion gas is cooled, the durability thereof canbe enhanced. The air which has passed through the flow guide 9 and theguide wall 12 for combustion gas passes through a lower air passage 23and is led into the combustor 15, where it is used as combustion air.

The combustion gas generated at the combustor 15 heats the outerreaction tube 2, flows through the combustion gas passage C, and isexhausted from the exhaust tube 27 to outside the reforming apparatus.

The heat insulating layer 29 prevents the loss of radiation from theinner wall 20 of the reforming apparatus to the atmosphere.

In this first embodiment, since the flow guide 9 is provided and airpassages surrounding the guide wall in a dual structure are provided, itis possible to reduce the temperature of the guide wall 12 forcombustion to an even lower level, thereby effectively reducing theradiation loss. In other words, the air passage A surrounding thehigh-temperature combustion gas passage C is cooled by the air whichflows therethrough, and the temperature of the members constituting theair passage can be reduced lower than the temperature of the constituentmembers of a combustion gas passage in a conventional structure which isnot provided with air passages. For example, the temperature of theouter surface of the reforming apparatus ranging from 600° to 1,000° C.can be lowered to the vicinity of the temperature of the supply air.

Accordingly, since the thickness of the heat insulating layer forpreventing the heat loss to the atmosphere can be made thin, the overalldimensions of the reforming apparatus can be made compact. Furthermore,the air which flows through the air passages and is heated by heatissuing from the combustion gas passage can be utilized for combustion,so that the heat loss can be reduced.

FIG. 2 shows a fuel reforming apparatus 1A in accordance with a secondembodiment of the present invention. This fuel reforming apparatusdiffers from the fuel reforming apparatus 1 shown in FIG. 1 in that anauxiliary combustion burner 40 is provided in a space formed by theguide wall 12 for combustion gas and the flow guide 9. The auxiliarycombustion burner 40 burns fuel by using the air flowing between theguide wall 12 for combustion gas and the flow guide 9. This auxiliarycombustion burner 40 is used to raise the temperature of the guide wall12 for combustion gas within a short time at the time of starting thefuel reforming apparatus. In particular, the auxiliary combustion burner40 is effective when a combustion catalyst which requires preheating isused for the combustor 15. Alternatively, an electric heater may be usedinstead of the auxiliary combustion burner. In this case, favorablecombustion takes place since the air temperature can be raised withoutchanging the rate of oxygen in the air which is supplied to thecombustor. The fuel reforming apparatus in accordance with this secondembodiment is advantageous in that the starting time can be shortened.

FIG. 3a shows a fuel reforming apparatus 1B in accordance with a thirdembodiment of the present invention. This fuel reforming apparatusdiffers from the fuel reforming apparatus 1 of the first embodimentshown in FIG. 1 in the following aspect:

A flow guide 9b is provided in a space between a guide wall 12b forcombustion gas and the inner wall 20 of the reforming apparatus, and aheat exchanger plate 50 is provided in a space between the inner wall 20of the reforming apparatus and the flow guide 9b (see FIG. 3b). The airsupply tube 18 communicates with an air manifold 51, which is turncommunicates with a part A of a space formed by the inner wall 20 of thereforming apparatus, the flow guide 9b, and the heater exchanger plate50. The other portion of the space formed by the inner wall 20 of thereforming apparatus, the flow guide 9b, and the transfer plate 50communicates with the combustion gas passage C by means of a combustiongas communicating hole 53 and also communicates with a combustion gasmanifold 54.

In operation, the air flows from the air supply tube 18 into the airmanifold 51, and flows into the space formed by the inner wall 20 of thereforming apparatus, the flow guide 9b, and the heat exchanger plate 50.Communicating holes may be provided in this space so that the airpassages A and combustion gas passages C' may be formed alternately. Theair which flows through the air passage A receives heat from thecombustion gas via the heat exchanger plate 50. The air which has flowedthrough the space passes through the air hole 52, flows into the spaceformed by the flow guide 9b and the guide wall 12b for combustion gas,cools the guide wall 12b for combustion gas, and is supplied to thecombustor 15 via the air passage 23 disposed below the combustor 15.

The combustion gas generated in the combustor 15 flows through thecombustion gas passage C, flows through the combustion gas passageformed by the flow guide 9b, the inner wall 20 of the reformingapparatus, and the heat exchanger plate 50, and preheats the air via theheat exchanger plate 50. The combustion gas with its temperature loweredflows into the combustion gas manifold 54, and is exhausted from anexhaust tube 55 for combustion gas to the outside.

According to this third embodiment, it is possible to reduce thecapacity of a device for recovering the heat of a combustion exhaust gassince the sensible heat of the combustion exhaust gas is recoveredinside the fuel reforming apparatus so as to be used as combustion air.

FIG. 4a shows a fuel reforming apparatus 1C in accordance with a fourthembodiment of the present invention. Description will be made hereafterof the fuel reforming apparatus lC with respect to its differences withthe fuel reforming apparatus in accordance of the first embodiment shownin FIG. 1.

A supporting plate 8c is jointed to a heat-exchange wall 60. Aterminating end of the heat-exchange wall 60 is formed as a flange 61and is fixed to a bottom plate 11c. A guide wall 12c for combustion gasis provided on the inner side of the heat-exchange wall 60 with a gaptherebetween, and a flange provided at one end thereof is secured to abottom plate 11c together with a flange 61 of the heat-exchange wall 60.Combustion passages C are formed in a space between the outer reactiontube 2 and the guide wall 12c for combustion and in a space between theguide wall 12c for combustion and the heat-exchange wall 60. A heatinsulating member 14 is disposed in contact with the flange 13c andalong the inner wall 12c for combustion gas up to a certain lengththereof. In addition, a supporting member 17c which also serves as aheat-insulating material is disposed between the combustor 15 and thebottom plate 11c. Furthermore, an air tube 18c and a fuel tube 19c forcombustion are connected to the combustor 15 in such a manner as topenetrate the bottom plate 11c and the supporting member 17c. An innerwall 20c of the reforming apparatus is disposed such as to surround theheat-exchange wall 60. The other end of the inner wall 20c of thereforming apparatus is welded to a semi-elliptical end plate 22c, and asupplying passage F for fuel gas is formed in a space between theheat-exchange wall 60 and the inner wall 20c of the reforming apparatus.Incidentally, a catalyst charging port 62 is provided in the end plate22c at a place slightly distant from the position where the innerreaction tube 3 is located. Several raw fuel tubes 25c for supplying rawfuel to a supplying passage F for fuel gas are provided in the bottomplate 11c. In addition, several exhaust tubes 27c are provided forintroducing the exhaust gas from the combustion gas passage C to outsidethe fuel reforming apparatus 1C.

FIG. 4b shows a cross-sectional view of the fuel reforming apparatus lCtaken along the line IVb--IVb of FIG. 4a. In this arrangement, the guidewall 12c, the heat-exchange wall 60, and the inner wall 20c of thereforming apparatus are disposed concentrically, but a plurality of thereaction tubes 4 of a double tube structure may be provided. Inaddition, although eight raw fuel tubes 25c and four exhaust tubes 27care provided symmetrically about a point, the number and arrangementthereof may be determined, as necessary.

The operation of this embodiment will now be described.

First, the air and the combustion fuel both preheated by the combustor15 are respectively led to the air tube 18c and the fuel tube 19c forcombustion, and the combustion fuel is burned in the combustor. Flame isformed by the nozzles 16 and generate a high-temperature combustion gas.The combustion gas flows through the combustion gas passage C betweenthe guide wall 12c for the combustion and the outer reaction tube 2.While raising the temperature of the reaction tube 4 of a double tubestructure and the reforming catalyst 6, the combustion gas flows throughthe combustion gas passage C between the heat-exchange wall 60 and theguide wall 12c for combustion gas, and is led from the exhaust tube 27cto outside the fuel reforming apparatus lC as an exhaust combustion gas.At that juncture, in order to effect a uniform temperature rise of thereaction tube 4 of a double tube structure as well as to reduce the timeduration of temperature rise, a preheated fluid, such as nitrogen, isallowed to flow from the raw fuel tube 25c via the supplying passage Ffor fuel gas until the temperatures of the reaction tube 4 and thereforming catalyst 6 rise to predetermined levels, while the reformingcatalyst 6 held in the reaction tube 4 of a double tube structure isheated directly. After directly heating the reforming catalyst 6, thefluid is led outside the fuel reforming apparatus 1C via the innerreaction tube 3. In addition, in the above-described process, whileflowing through the supplying passage F for fuel gas, the fluid fordirectly heating the reforming catalyst 6 receives heat and is heatedthrough the heat-exchange wall 60 by the combustion gas flowing in thecombustion gas passage C between the heat-exchange wall 60 and the guidewall 12c for combustion gas.

In other words, a heat-exchange portion 32c, which constitutes a featureof the present invention, is formed by virtue of the arrangement of theguide wall 12c for combustion gas, the heat-exchange wall 60, and theinner wall 20c of the reforming apparatus.

After the reaction tube 4 of a double tube structure and the reformingcatalyst 6 reach predetermined temperatures, the fluid which is allowedto flow through the raw fuel tube 25c is changed over to a raw fuel inwhich, for instance, preheated methane and steam are mixed. Uponentering the fuel reforming apparatus 1C, the raw fuel is heated by thecombustion gas, and is converted to a hydrogen-enriched gas in the layerin which the reforming catalyst 6 is filled. The hydrogen-enriched gasthen passes through the inner reaction tube 3 and is discharged tooutside the fuel reforming apparatus lC.

According to this fourth embodiment, since heating of a high temperaturelevel can be effected from inside and outside of the reaction tube of adouble tube structure at the time of increasing the temperature of thefuel reforming apparatus, there is an advantage in that the timeduration required for increasing the temperature, i.e., the rise time,can be shortened. In addition, since the heat exchange can be effectedbetween the raw fuel and the combustion gas in the fuel reformingapparatus during a normal operation, there is an additional advantage inthat a preheater for the raw material fed from the outside can be madecompact.

FIG. 5a shows a fuel reforming apparatus 1D in accordance with a fifthembodiment of the present invention. Description will be made hereafterof its differences with the fuel reforming apparatus 1C in accordancewith the fourth embodiment shown in FIG. 4a.

In FIG. 5a, drift preventing plates 63 jointed to a heat-exchange wall60d are provided inside a supplying passage F for fuel gas in such amanner as to project vertically from a bottom plate 11d. Thisarrangement is a characteristic feature of this embodiment. Each of thedrift preventing plates 63 is arranged in such a manner that onelongitudinal end thereof abuts against the bottom plate 11d, and theother end thereof projects from a supporting plate 8d toward the side ofan end plate 22d. As shown in FIG. 5b, the drift preventing plates 63are respectively disposed at central positions between adjacent rawmaterial tubes 25d disposed on the bottom plate 11d. Each of the driftpreventing plates 63 has a slight gap between the same and an inner wall20d of the reforming apparatus and is thereby adapted to prevent thecollision between the drift preventing plate 63 and the inner wall 20dof the reforming apparatus owing to thermal expansion.

By virtue of the above-described arrangement, the raw material fed fromthe raw fuel tubes 25d into the fuel reforming apparatus 1D is led intothe space between the supporting plate 8d and the end plate 22d, while acertain flow rate is maintained in a supplying passage F for fuel gassurrounded by the inner wall 20d of the reforming apparatus, theheat-exchange wall 60d, and the adjacent drift preventing plates 63.Subsequently, the raw fuel passes through the layer charged with thereforming catalyst 6, and is discharged outside the fuel reformingapparatus lD as a hydrogen-enriched gas.

According to the fifth embodiment, if members having good thermalconductivity are used as the drift preventing plates, since the driftpreventing plates serve as fins for transmitting heat from thecombustion gas to the raw fuel, the raw fuel is heated more effectively.Hence, in addition to the advantages of the fourth embodiment shown inFIG. 4a, there are advantages in that the rising time of the fuelreforming apparatus can be further reduced, and that an externalpreheater for preheating the raw fuel can be made more compact.

FIG. 6a shows a fuel reforming apparatus 1E in accordance with a sixthembodiment of the present invention. Description will be made hereafterof its differences with the fuel reforming apparatus 1C according to thefourth embodiment shown in FIG. 4.

In FIG. 6a, an inner wall 20e of the reforming apparatus and asemi-elliptical end plate 22e are not welded to each other, but arerespectively provided with flanges 65, 66 and are flange-connected toeach other. A catalyst supporting plate 67 is welded to the inner wall20e of the reforming apparatus such as to surround a heat-exchange wall60e. A reforming catalyst 68 is filled in the supplying passage F forfuel gas from the catalyst supporting plate 67 toward the end plate 22eside. The catalyst supporting plate 67 is provided with a hole 69, and aslight gap is provided between the catalyst supporting plate 67 and theheat-exchange wall 60e. By virtue of the above-described arrangement,the raw fuel flowing into the supplying passage F for fuel gas throughthe raw fuel tube 25e passes the heat-exchange wall 60e, and receivesheat transmitted from the combustion gas to the reforming catalyst 68side via the heat-exchange wall 60e. Hence, the raw fuel is subjected tothe aforementioned reactions (1) and (2) while being brought intocontact with the reforming catalyst 68. One condition for obtaining amaximum reforming rate of the raw fuel is to retain these reactions atapproximately 800° C. or above. However, the temperature of the layercharged with the reforming catalyst 68 does not reach that level.Therefore, unreformed raw fuel is reformed in the layer charged with thereforming catalyst 6 in the reaction tube 4 of a double tube structure,and is converted to a desired hydrogen-enriched gas before it isdischarged outside the fuel reforming apparatus lE. FIG. 6b shows across-sectional view taken along the line VIb--VIb of FIG. 6a.

According to the sixth embodiment, since the temperature of the innerwall 20e of the reforming apparatus with which the reforming catalyst isbrought into contact in conjunction with the endothermic reaction in thereforming catalyst-charged layer 68, there is an advantage in that thelife of the inner wall 20e of the reforming apparatus with respect tothe temperature is improved.

FIG. 7a shows a fuel reforming apparatus 1F in accordance with a seventhembodiment of the present invention. Description will be made hereafterof its differences with the fuel reforming apparatus 1E according to thefifth embodiment shown in FIG. 6a.

In FIG. 7a, drift preventing plates 70 jointed to a heat-exchange wall60f are disposed in the supplying passage F for fuel gas in which thereforming catalyst 68 is accommodated, in such a manner as to projectvertically from a bottom plate 11f. One longitudinal end of each of thedrift preventing plates 70 penetrates the catalyst supporting plate 67,and abuts against the bottom plate 11f, while the other end thereofprojects from a supporting plate 8f toward the side of an end plate 22f.FIG. 7b is a cross-sectional view taken along

the line VIIb--VIIb of FIG. 7a. Incidentally, each of the driftpreventing plates 70 has a slight gap between the inner wall 20f of thereforming apparatus and the catalyst supporting plate 67 so as toprevent the collision therebetween at the time of thermal expansion. Byvirtue of the above-described arrangement, the amount of influx of theraw fuel from raw fuel tubes 25f into the layer filled with thereforming catalyst 68 inside the supplying passage F for fuel gas isdistributed uniformly. Upon completion of reaction with the reformingcatalyst 68, the gas containing unreacted raw fuel passes through thelayer filled with the reforming catalyst 6, is converted to ahydrogen-enriched gas, and is discharged to outside the fuel reformingapparatus 1F.

According to the seventh embodiment, since the uniform reaction with thereforming catalyst is promoted, in addition to the advantages of thesixth embodiment shown in FIG. 6a, there are advantages in that there isno unevenness in some reforming catalyst, and that the life of theoverall reforming catalyst is prolonged as a result.

FIG. 8 shows a fuel reforming apparatus 1G in accordance with an eighthembodiment of the present invention. This fuel reforming apparatus issimilar to the fuel reforming apparatus 1E shown in FIG. 6a, but differsfrom the same in the following aspects.

In the fuel reforming apparatus 1G shown in FIG. 8, a guide wall forcombustion gas is not provided, and the combustion gas is dischargedoutside the fuel reforming apparatus lG through bellows 80 providedpenetrating a supporting plate 8g. At that juncture, since each of thebellows 80 is flange-connected to an upper cover 81 which isflange-connected to an inner wall 20g of the reforming apparatus, ahighly reliable material which is sufficiently capable of following thethermal expansion or shrinkage of a heat-exchange wall 60g and the uppercover 81 at a temperature of about 650° C. is used as the bellows 80. Inthe upper cover 81, exhaust tubes 82 for discharging the combustion gasare adapted to form combustion gas passages with the upper cover 81placed between the exhaust tubes 82 and the bellows 80. In addition, aparticle supporting plate 83 is welded to the heat-exchange wall 60g inthe combustion gas passage C between the outer reaction tube 2 and theheat-exchange wall 60g. As a result, heat conductance accelerationparticles (alumina particles) 84 are supported by the particlesupporting plate 83 toward the supporting plate 8g. Accordingly, thebellows 80 are also used as ports for charging the heat conductanceaccelerating particles 84. The flow rate of the fuel gas is acceleratedby the presence of the heat conductance accelerating particles. Byvirtue of the above-described arrangement, heat conductance from thecombustion gas to the reforming catalysts 6 and 68 is accelerated.

According to the eighth embodiment, since the guide wall for combustiongas and the combustion gas passage C between the guide wall forcombustion gas and the heat-exchange wall 60g are dispensed with, thereis an advantage in that the fuel reforming apparatus becomes slender, sothat a space for installing the apparatus can be small.

What is claimed is:
 1. A fuel reforming apparatus, comprising:a reactiontube means forming a volume where an endothermic reaction for convertinga fuel gas, with steam mixed therein, into hydrogen-enriched gas, usinga catalyst, occurs, with said volume including means for retaining acatalyst therein, said reaction tube means having an inlet means fortransmitting fuel gas with steam mixed therein into the volume andoutlet means for removing hydrogen-enriched gas from the volume; acombustor for generating a combustion gas, to heat said reaction tubemeans; combustion gas passage means for passing said combustion gasadjacent said reaction tube means so as to heat said reaction tubemeans, said combustion gas passage means being positioned around thevolume, said combustion gas passage means including a combustion gasoutlet means for discharging combustion gas from the fuel reformingapparatus, the inlet means for transmitting fuel gas with steam mixedtherein into the volume including a fuel gas supplying passage meansdisposed around the combustion gas passage means and in heat exchangerelationship with the combustion gas passage means, the fuel gassupplying passage means having means for retaining a catalyst therein;fuel passage means for supplying fuel to the combustor; air passagemeans for supplying air to the combustor; and insulating layer means forpreventing heat radiation from the fuel forming apparatus, theinsulating layer means being disposed around the fuel gas supplyingpassage means.
 2. A fuel reforming apparatus according to claim 1,further comprising a catalyst filling said volume, and retained thereinby said means for retaining a catalyst therein.
 3. A fuel reformingapparatus according to claim 2, further comprising a catalyst fillingsaid fuel gas supplying passage means, and retained therein by the meansfor retaining a catalyst in the fuel gas supplying passage means.
 4. Afuel reforming apparatus according to claim 1, further comprising acatalyst filling said fuel gas supplying passage means, and retainedtherein by the means for retaining a catalyst in the fuel gas supplyingpassage means.
 5. A fuel reforming apparatus according to claim 1,wherein the fuel gas supplying passage means and the combustion gaspassage means have a common heat-exchange wall providing theheat-exchange relationship between the fuel gas supplying passage meansand the combustion gas passage means.
 6. A fuel reforming apparatusaccording to claim 5, further comprising a catalyst filling said volume,and retained therein by said means for retaining a catalyst therein. 7.A fuel reforming apparatus according to claim 6, further comprising acatalyst filling said fuel gas supplying passage means, and retainedtherein by the means for retaining a catalyst in the fuel gas supplyingpassage means.
 8. A fuel reforming apparatus according to claim 1,wherein the combustion gas passage means comprises means for retainingheat conductance acceleration particles in said combustion gas passagemeans adjacent said reaction tube means.
 9. A fuel reforming apparatusaccording to claim 8, further comprising heat conductance accelerationparticles in said combustion gas passage means, adjacent said reactiontube means, retained in the combustion gas passage means by said meansfor retaining heat conductance acceleration particles.
 10. A fuelreforcing apparatus according to claim 9, wherein said combustion gasoutlet means includes bellows means.
 11. A fuel reforming apparatusaccording to claim 1, further comprising drift preventing platesdisposed in said fuel gas supplying passage means.
 12. A fuel reformingapparatus according to claim 1, wherein the reaction tube means has adouble tube structure, said volume being between the two tubes of thedouble tube structure.